METHODS: Subjects with HCM (n=9), hypertensive heart disease (HHD, n=9) and normals (n=9) underwent heart sound frequency analysis (HSFA) and electrocardiography (ECG). An electronic stethoscope was used to record heart sounds for 6 seconds in the lying down (LD), standing (S) positions and post exercise (E). Fast Fourier analysis of the heart sound recordings was performed and frequency peaks were analyzed using MATLAB software. Change in frequencies from LD to S and LD to E were evaluated. The data was statistically analyzed using t-test. The results of the frequency analysis were compared to the results of the ECG.

RESULTS: Widening of the frequency spectrum of heart sounds upon standing identified the majority of subjects with HCM. 88.9% of HCM subjects showed an increase in the range of frequencies from LD to S (average change = +57.74 Hz). In comparison, 88.9% of normal subjects displayed a significant decrease in the range of frequencies (average change = - 27.2 Hz, p-value = 0.01). 88.9% of subjects with HHD also showed a significant decrease in the range of frequencies upon standing (average change = -38.62 Hz, p-value=0.008). No significant differences were found between the normal and HHD group (p-value=0.64). HSFA had a high specificity and sensitivity of 88.9% each. ECG with a 100% specificity and 38.9% specificity was unable to identify the majority HCM subjects (false negative rate 61.1%). At a cut off of 20 Hz the estimated accuracy of HSFA is 99.93%.

CLINICAL IMPLICATIONS: AHA/ACC acknowledges the limited public health benefit of universal ECG screening in HCM on account of its high false positive and negative rates. Early detection of HCM is key to preventing sudden cardiac death. Heart sound frequency analysis is inexpensive, easy to perform in a public health setting and has the attributes of an ideal screening test.

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